vdk-core: inject parsed subsection configs into ConfigBuilder and support fetching by subsection

[DeltaMichael]

Prerequisites

#3305

Overview

The parsed vdk subsection configs should be injected into the ConfigBuilder. We should also have a way to fetch the configurations by subsection key from the Config object built by the ConfigBuilder.

Suggested Implementation

    @hookimpl(tryfirst=True)
    def vdk_configure(self, config_builder: ConfigurationBuilder) -> None:
            
            for section, conf in job_config.get_vdk_options().items():
                if section is not "vdk":
                    for k, v in conf.items():
                            config_builder.add(
                                 section=section
                                 key=k,
                                 default_value=v,
                                 description=description,
                             )
               else:
                    for k, v in conf.items():
                        config_builder.set_value(section="vdk", k, v)

We should have some kind of section -> config mapping in ConfigBuilder and Config. This should be backwards-compatible. For example, if we don't pass a section, we should just default to the "vdk" section. We won't have to change any other calls to set_value this way. Same goes for add.

We should also support fetching config values by section and key, or fetching whole config objects by section name. Fetching whole config objects by section name would help with implementing multiple dbs in plugins.

Acceptance criteria

1. Do the above implementation or a better alternative
2. Add tests